1.Field of the Invention
The invention disclosed herein relates to exploration for hydrocarbons and, in particular, to the evaluation of shale deposits.
2.Description of the Related Art
Shale gas reservoirs have been a source of natural gas for U.S. industry since its earliest days. As gas prices increase, unconventional gas development plays a larger role in the gas supply. While gas demand continuously grows and conventional reservoirs deplete, unconventional plays provide an increasingly significant contribution to the overall gas supply. It is clear this trend will continue into the future.
In the quest for gas, many types of geologic materials and formations are encountered. A descriptive term for characterizing the many types is that of “facies.” As commonly used, a facies is a body of rock with specified characteristics. Ideally, a facies is a distinctive rock that forms under certain conditions of sedimentation, reflecting a particular process or environment.
Identifying and characterizing the individual facies in shale gas reservoirs is a key towards understanding and predicting potential reservoir productivity. Each zone or interval facies is unique in its geochemical, petrophysical, and mineralogical properties. All of these properties influence the geomechanical properties of each facies. The geomechanical properties of facies are especially important because hydraulic fracturing is a method frequently used to stimulate and enhance gas productivity. Thus, detecting changes in rock integrity aid in planning these stimulation procedures. While a variety of technologies are useful for such detection, ever improved technologies are needed.
Therefore, what are needed are improved techniques for detecting changes in the integrity of shale deposits. Preferably, the techniques provide for developing a strategy for fracturing the shale deposits, which is based upon an understanding of the geomechanical properties of the facies, and results in not only saved costs during initial fracture, but may also can reduce the number of wells which require re-stimulation.